Highly fuel efficient gas burning water and/or space heating appliances, generally known as power burner, power assist, or power chamber type appliances, have been recently developed which are provided with powered or forced draft combustion systems employing a blower for forcing the gas/air combustion mixture to the burner and into the combustion chamber of the heating appliance. One such high efficiency power assist water heating appliance is disclosed in U.S. Pat. No. 4,766,883 to Cameron et al., which patent is assigned to the same assignee as that of the present application and the disclosure of which is incorporated herein by reference. This patent discloses a water heating apparatus in which a combustible gas/air mixture is introduced into a blower which moves the mixture under pressure into a vertically extending tubular burner within a closed combustion chamber contained within a tank containing water. The products of combustion exit the combustion chamber and pass through a helical tube of several turns within the body of water. The heat of combustion is extracted from the products of combustion by conduction through the walls of the combustion chamber and the helical exhaust tube. A high efficiency water heater thereby results. The heated water from the water heater may also be used to heat the air of a home or building by piping the hot water to a heat exchanger contained within the ducts of the home ventilation or heating system.
While this apparatus provides a highly efficient water and/or air heater, certain problems nevertheless are present. Thus, in the closed combustion chamber of such an apparatus assisted with a blower, the ignition of the gas/air mixture, when it is first introduced into the combustion chamber from the burner, is often delayed. This delay is due to factors such as the size and arrangement of the combustion chamber, the velocity and temperature of the combustible gas/air mixture entering the chamber, and the location of the ignition source. Depending on the length of the delay, an explosion may occur that ranges in magnitude from a small backlash to a forceful one that could damage the appliance. In some instances, this delay can be controlled by directing the gas/air mixture from the burner toward the ignition source in the combustion chamber as the mixture enters the chamber.
In general, however, even at the smoothest of ignition of the gas/air mixture, a delay may be present that causes a phenomenon which is known as sputtering. This is caused by the back pressure created by the initial ignition of the gas/air mixture. When the mixture is first ignited, the product of combustion occupies more volume than the mixture originally had occupied. This exerts a back pressure on the incoming mixture which in effect starves the chamber of combustible mixture. This in turn causes a momentary flame outage and a break in the combustion process. The blower, however, overcomes the back pressure and the gas/air mixture enters the combustion chamber and reignites. This process, producing a sputtering effect, is repeated a few times until the blower overcomes the back pressure of ignition and continuous combustion then occurs.